The goal of our research is to determine the primary sequence of the envelope glycoprotein gp70 from endogenous and recombinant retroviruses of AKR mice. We wish to define the constant and variable portions of the molecules and determine where the recombinational event takes place. Parallel studies show a correlation with the onset of leukemia and the appearance of leukemogenic recombinant viruses with alteration in their gp70's. We wish, therefore, to define unique regions within the AKR recombinant virus gp70's and compare these to recombinant viruses of other systems. In this way, we can begin to relate specific structural changes to the unique properties of the recombinant viruses.